Patent GB-772432-A (GB)
Title: Gyroscopic instruments
IPC: G01C19/38
Filed: 1955-04-13
Abstract: 772,432. Gyroscopic compasses. SPERRY RAND CORPORATION. April 13, 1955 [May 25, 1954], No. 10642/55., Class 97(3) In a gyro compass comprising a rotorbearing frame containing a rotor and mounted with freedom of angular movement about a normally horizontal axis in a vertical ring, which is itself mounted with freedom of angular movement about a normally vertical axis in an instrument housing, the housing is completely filled with liquid, the rotor-bearing frame completely surrounds the rotor, has external symmetry, is liquid-tight and, together with the vertical ring, is completely immersed in the liquid, the densities of the rotor-bearing frame and the vertical ring being each substantially equal to the density of the liquid, whereby their weights are supported in neutral equilibrium by the buoyancy forces of the liquid. As shown in Fig. 1, a gyro compass of small size is housed in binnacle 10 comprising a main compartment 11 with a transparent cover 17. The card 18 of the compass element is visible through the cover 17 and is readable against a lubber line or mark 19. The hole of the binnacle 10 is filled with a liquid such as kerosene in which the operating parts of the instruments float. Liquid connection is made through a tube 22 to an expandable diaphram 14. Electrical connections for the instrument are made through a socket 24. Rotor mounting. The rotor 27, Fig. 5, is driven by a squirrel cage induction motor having a stator 31 and a cage 32, and is mounted for rotation about a normally North-South axis 30 in a spherical casing 26 which is hermetically sealed and substantially evacuated. Liquid ballistic. The meridian seeking torque of the gyro compass is provided by a liquid ballistic comprising a pair of toroidal shaped tanks 34, 35 located within the liquid tight case 26, and connected by a tube 36 having a central portion 37 of reduced cross-sectional area. The top of the tanks 34, 35 are connected by a breather tube 38. The tanks 34, 35 'are half-filled with a liquid such as carbon tetrachloride the free-liquid surface area (which is maintained constant when the casing 26 tilts about its East-West axis by the toroidal shape of the tanks 34, 35) of which is designed to give approximately an 85 minute period for the gyro compass. Mounting of rotor casing. The casing 26 is mounted about normally horizontal ax's 41 in a gimbal ring 39, Fig. 1, which is in turn mounted about a normally vertical axis 40 in the binnacle 10. The weight of the components in the casing 26 is such that it just floats in the liquid in binnacle 10, so as to minimize friction in the bearings. Two of the three phase current windings for the rotor driving motor are lead into the gimbal through the lower bearing 46, while the third wire is lead in through the upper bearing 47. The wires are lead through the bearings of the rotor casing by means of brushes 109, 110, 111. An upper float tank 55 and a lower float tank 56 are connected to the gimbal ring 39 and are so designed that the floats and ring just float in the liquid contained in the binnacle 10. Both float chambers are symmetrical about the vertical axis 40, and the upper chamber 55 supports the compass card 18. Damping means. The damping means includes a compound pendulum located on the northerly disposed side of the case 26. As shown in Figs. 5 and 6, a first pendulum 62 is mounted for rotation about the North-South axis 30. The second pendulum 66 is mounted on the pendulum 61 to pivot about an axis 67. Pendulum 66 extends around the pendulum 62, and has a float chamber 72 containing a liquid in which moves a paddle 71 fixed to the pendulum 62. An impeller 80, driven through a magnetic coupling from the shaft of the rotor 27, draws in the surrounding floatation liquid and expels it through channel 79 in the pendulum 62. Channel 79 communicates with a channel 78, from which the liquid passes to channels 76, 77 in the pendulum 66. The liquid emerges from these channels in opposite direction, and the streams encounter blade 89, 90 mounted on the pendulum 62. When the East-West axis 41 of the compass is horizontal, the streams of liquid impinge equally on the vanes and no torque results. Should the casing tilt about the axis 41, one of the liquid streams is intercepted more by one vane and less by the other; so that a torque results which precesses the gyro to restore the axis 41 to the horizontal. Anti-swirl device.. If the instruments should turn in a uniform direction for a considerable time, the liquid in the binnacle 10 acqures a rotational movement which exerts a torque on the casing 26. To counteract this torque, a curved blade 91 is mounted 'below the pendulum 66, in such a manner that the movement of the liquid in the binnacle acting on the blade 91 moves the pendulum 66 to cover or uncover the channel 76, 77. The resultant torque opposes and counteracts the torque course by the swirling of the liquid. A mass 63, Fig; 5, is mounted at the south side of the casing 26 to counteract the weight of the pendulum 62, 66. Re-setting means. A re-setting .knob 94 is mounted on a shaft 95 extending through a mounting 96 set in the wall of the binnacle 10. Shaft 95 is rotatable, and is also movable axially between two positions defined by grooves 100, 101 engaged by a spring pressed ball 99. As shown, groove 100 is engaged by the ball 99, and the knob is in its inoperative position, inasmuch as a straight washer 105 and a curved washer 106 are clear of the float chamber 56. When the knob 94 is pressed forward so that the groove 101 is engaged by the ball 99, the curved washer 106 is pressed flat and through it the washer 105 engages a ring 102 formed on the rim of the float chamber 56. Freedom of movement about the vertical axis 40 is lost, and by turning the knob the position on the compass card 18 can be set as desired. If the rotor is spinning, this adjustment results in the tilt of the casing 26 about its axis 41. Tilt about axis 41 may be corrected by moving the knob into the intermediate position where ball 99 lies between the grooves 100, 101. In this position the ring 102 on float chamber 56 is engaged lightly by the curved washer 106. The loose frictional coupling allows torque to be applied which results in the levelling of the casing 26 about its axis 41. To assist in levelling, a number of liquid level devices, of which are indicated at 108, 101, are symmetrically arranged on the casing 26 and are observed through the transparent dome 17. Specification 772,433 is referred to.